From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 3491BC4332F for ; Tue, 31 Oct 2023 13:18:42 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1qxodQ-0001wy-Jr; Tue, 31 Oct 2023 09:18:20 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1qxodP-0001wW-8L for qemu-devel@nongnu.org; Tue, 31 Oct 2023 09:18:19 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1qxodN-0000vq-Vx for qemu-devel@nongnu.org; Tue, 31 Oct 2023 09:18:19 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1698758297; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=RQgbpbhe06eH1hJLCzobEgsuAcsHm4lCj9WiyDgKUrE=; b=hE7O+NQ5yNNmEXhbQtBaQwgp3uk2EuPdIgAVQPhXYX1yX7xFmQHsfOmlEhjV46WsmOdiM2 7fTEwrefm8kKNDor6v5YFIc4B41eryPdfANCyVPdTElzioB+I1IHmktgFGYSAsepEv+8jk EX2OPmXb8iE4eE36m638qR73zQTYIGE= Received: from mimecast-mx02.redhat.com (mx-ext.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-502-VTdWBVAZPYi4QUxakUH6Mw-1; Tue, 31 Oct 2023 09:18:01 -0400 X-MC-Unique: VTdWBVAZPYi4QUxakUH6Mw-1 Received: from smtp.corp.redhat.com (int-mx10.intmail.prod.int.rdu2.redhat.com [10.11.54.10]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 13B571C0BA5B; Tue, 31 Oct 2023 13:18:00 +0000 (UTC) Received: from redhat.com (unknown [10.39.194.218]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 08BD5492BFC; Tue, 31 Oct 2023 13:17:57 +0000 (UTC) Date: Tue, 31 Oct 2023 14:17:56 +0100 From: Kevin Wolf To: Philippe =?iso-8859-1?Q?Mathieu-Daud=E9?= Cc: qemu-devel@nongnu.org, Paolo Bonzini , Hanna Reitz , Fam Zheng , qemu-arm@nongnu.org, "Michael S. Tsirkin" , qemu-block@nongnu.org, Jason Wang , Peter Maydell , Raphael Norwitz , "Edgar E. Iglesias" , Alistair Francis , Gerd Hoffmann , rjones@redhat.com Subject: Re: [PATCH 4/7] hw/scsi/virtio-scsi: Use VIRTIO_SCSI_COMMON() macro Message-ID: References: <20231017140150.44995-1-philmd@linaro.org> <20231017140150.44995-5-philmd@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20231017140150.44995-5-philmd@linaro.org> X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.10 Received-SPF: pass client-ip=170.10.133.124; envelope-from=kwolf@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -25 X-Spam_score: -2.6 X-Spam_bar: -- X-Spam_report: (-2.6 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.481, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Am 17.10.2023 um 16:01 hat Philippe Mathieu-Daudé geschrieben: > Access QOM parent with the proper QOM VIRTIO_SCSI_COMMON() macro. > > Signed-off-by: Philippe Mathieu-Daudé > --- > hw/scsi/virtio-scsi.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/hw/scsi/virtio-scsi.c b/hw/scsi/virtio-scsi.c > index 45b95ea070..fa53f0902c 100644 > --- a/hw/scsi/virtio-scsi.c > +++ b/hw/scsi/virtio-scsi.c > @@ -761,7 +761,7 @@ static void virtio_scsi_fail_cmd_req(VirtIOSCSIReq *req) > > static int virtio_scsi_handle_cmd_req_prepare(VirtIOSCSI *s, VirtIOSCSIReq *req) > { > - VirtIOSCSICommon *vs = &s->parent_obj; > + VirtIOSCSICommon *vs = VIRTIO_SCSI_COMMON(s); > SCSIDevice *d; > int rc; Why is a dynamic cast more "proper" than a static type-safe access, even more so in a hot I/O path? Rich Jones posted a flamegraph the other day that surprised me because object_class_dynamic_class_assert() and object_dynamic_cast_assert() were shown to be a big part of scsi_req_new(). In the overall performance, it's probably dwarved by other issues, but unnecessary little things can add up, too. Kevin